This invention relates generally to boiler cleaning machines and more particularly to cleaning machines such as water deslaggers and soot blowers having a rotary lance which reciprocates out from and back into a housing outside the boiler.
The operation of boilers for steam power plants, particularly using coal of lower grade, results in the gradual build-up of various materials on the interior surfaces of the boiler exposed to flame. In some cases, the coating that builds-up is merely soot particles which adhere strongly to the surfaces, but the use of certain types of coal results in the build-up of a slag material on the hotter surfaces. In order to maintain peak boiler efficiency, it is necessary to periodically keep cleaning off these deposits to eliminate their insulating effect to insure maximum heat conduction between the flame and the boiler surfaces generating steam. While some materials such as soot can be removed with a blast of compressed air or steam, slag generally requires a water spray which will cool the hot slag, and by causing it to crack from temperature differentials will allow it to flake away and drop to the bottom of the boiler where it can be removed.
This type of cleaning is generally accomplished by means of a moving lance having a nozzle at the front end thereof which is moved into and out of the boiler chamber while rotating to spray the steam or water directly on the surfaces to be cleaned. Generally, the cycle of extension and retraction does not take more than several minutes to avoid excessive exposure of the lance to the heat within the boiler chamber, while the mechanism for moving the lance is supplying it with cleaning fluid remains outside the boiler.
There are many mechanisms that have been proposed for moving the lance in and out of the boiler and the selection of these mechanisms may depend upon the frequency in which the cleaning lance is cycled as well as the length the lance projects into the boiler or its total length of travel. While generally cables are used to traverse a carriage on relatively long lances, other mechanisms such as chains and racks may be used to traverse the carriage carrying the lance in and out of the boiler. The mechanism that provides power for moving the carriage also rotates the lance so that it is effectively rotationally driven by a gear arrangement driven by the carriage reciprocating mechanism. One of the problems with this arrangement is that because of the geared relationship and the fact there is generally one or two spray nozzles on the tip of the lance, these nozzles tend to travel over the same path on each cleaning cycle and this tends to limit the area being cleaned in direct alignment with the nozzle. Because of the rate at which the cleaning fluid is sprayed, the rotational speed of the lance is limited to insure complete coverage of the area under the nozzle, and to cover the entire areas in the helical path that results generally requires an excessive rotational number of turns per unit of lance movement. This would tend to mean a very tight helix which might require excessive time of exposure within the boiler.
One alternative to this is to provide a lost motion connection in the drive between the advance and retract so that by taking up the lost motion the retraction helix is shifted from the advancing helix to provide more complete coverage of the area being cleaned. However, this still leaves only two different patterns for the spray, and this may still leave much of the area untouched by the cleaning fluid.